Overview
PDW quantifies variation in platelet volume (analogous in concept to RDW for red cells).
Clinical Importance
As a supportive platelet index with count and MPV
Specimen Requirements
- Specimen: whole blood
- Tube: lavender-top K₂EDTA (preferred) or K₃EDTA
- Anticoagulant: EDTA
- Handling: invert gently 8–10 times immediately after draw; do not shake
- Storage: room temperature preferred for prompt analysis; follow analyzer/manufacturer limits
- Stability: analyze as soon as practical (many CBC parameters are stable for several hours at room temperature; verify local procedure). MPV increases with EDTA storage time. Do not freeze whole blood for CBC.
Analytical Method
Calculated from the platelet volume distribution width on automated hematology analyzers.
Instruments Used
Automated analyzers
- Sysmex XN / XN-L series hematology analyzers
- Beckman Coulter DxH series hematology analyzers
- Abbott Alinity hq / CELL-DYN hematology analyzers
- Siemens Healthineers ADVIA hematology analyzers
- Mindray BC-series hematology analyzers
- HORIBA Yumizen / ABX hematology analyzers
Manual methods
- Not a manual assay
Reference Values
Typical adult SI examples below follow widely published international hematology practice (e.g., Dacie and Lewis; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and altitude intervals differ.
Intervals are analyzer-specific; do not transpose published cutoffs across platforms.
Interpretation
Common Causes of Increased Results
- Increased PDW indicates more heterogeneous platelet sizes; nonspecific
Common Causes of Decreased Results
- Lower PDW suggests more uniform platelet volumes; nonspecific
Clinical Significance
- Adjunct platelet index on CBC reports where offered
Factors Affecting Results
Pre-analytical
- EDTA time and clumping affect platelet histograms
Analytical
- Method-specific algorithms
Post-analytical
- Overcalling clinical significance from isolated PDW changes
Advantages and Limitations
Advantages
- No extra specimen when included in CBC
Limitations
- Limited standalone clinical specificity
- Poor cross-platform transferability
Clinical Pearls
PDW is a histogram descriptor; it does not replace smear review for giant platelets or clumps.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Rodak BF, Carr JH. Rodak's Hematology: Clinical Principles and Applications. 6th ed. Elsevier; 2020.
- Hoffbrand AV, Moss PAH, Pettit JE. Essential Haematology. 8th ed. Wiley-Blackwell; 2019.
- McKenzie SB, Williams JL. Clinical Laboratory Hematology. 4th ed. Pearson; 2022.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
- Kaushansky K, et al. Williams Hematology. 10th ed. McGraw-Hill; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Validation, Verification, and Quality Assurance of Automated Hematology Analyzers; Approved Standard. CLSI document H26-A2. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Reference Leukocyte (WBC) Differential Count (Proportional) and Evaluation of Instrumental Methods; Approved Standard. CLSI document H20-A2. CLSI; 2007.
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Management of Critical- and Significant-Risk Results. CLSI guideline GP47-Ed1. CLSI; 2015.
Frequently Asked Questions
Common questions about using this Platelet Distribution Width (PDW) laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the Platelet Distribution Width (PDW) laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of Platelet Distribution Width (PDW). Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find Platelet Distribution Width (PDW) specimen requirements?
See the Specimen Requirements section on this page for specimen information related to Platelet Distribution Width (PDW). Confirm collection details against your laboratory protocol.
Where are Platelet Distribution Width (PDW) reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret Platelet Distribution Width (PDW) results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for Platelet Distribution Width (PDW)?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from Platelet Distribution Width (PDW)?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading Platelet Distribution Width (PDW)?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Hematology topic.
What are the clinical pearls for Platelet Distribution Width (PDW)?
See the Clinical Pearls section for concise laboratory practice notes associated with Platelet Distribution Width (PDW). Apply pearls alongside institutional protocols.
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